Pitch control means for sustaining rotors



Jaws, 1946.

. S. P. NEMETH PITCH CONTROL MEANS FOR SUSTAINING ROTORS Filed Aug. 20,i945 SPNEMETH FIG .4

Patented July 23, 1946 "PITCH CONTROL MEAN no'roas s FOR SUSTAININGStephan Paul N emeth, Chicago, Ill. Application August 20, 1943, SerialNo. 499,340

I the control of the pilot.

The pitch angle variation-features under the control of the pilot areintended to reduce the flapping angle and to provide pitch and rollcontrol of the aircraft in a known manner. The flapping is principallyrelied on for stabilizing the rotor and for preventing excessivecentrifugal loads and stresses. A periodic pitch angle variation of aperiod equal to that of the rotor rotation having an amplitude under thecontrol of the pilot is used'for providing an approximate balancebetween the left side and the right side of the rotor, that is to sayfor an approximate equalization of the lift of the advancing blade andof the retreating blade. A variation of the average blade pitch angleunder the control of the pilot is provided for goveming the mode offlying, whether the aircraft is predominantly flying forwardly with itsbest speed or whether it shall predominantly climb or hover at a lesseror no speed.

The inner portions of rotating blades do not produce lift commensuratewith the lift produced by their outer portions, because the velocity ofrotation of the inner blade portions is much smaller than the velocityof rotation of the outer blade portions. The lift production istherefore practically concentrated within an outer ring portion of thecircular disc" area through which the blades rotate. In consequence,there is produced on the left side and on the right side of the aircraftmore lift, and at the center portion of the disc circle, near thefuselage path, less lift than would be desirable for best efficiency. It

is a first object of my invention to provide a sustaining rotorproducing a more advantageous lift distribution crosswise the aircraft,favoring the portion near the flight path of the fuselage to a largerextent than present rotors do.

4 Claims. (01. 244-173 pacitycan-not be fully utilized because the liftof the advancing blade must balance and not over balance the lift of theretreating-blade. Thus, the lift capacity oi'the advancing blade ispartly wasted, to the detriment of its efficiency. Thisparticular-shortcoming also inherent in the presently described improvedrotor. But furthermore, with conventional rotors, the blade whenpointing forwardly into the direction of flight, .or rearwardly into atailwise direction, is arranged to produce a lift half waybetween thelift corresponding to the true lift capacity of the advancing blade andthe true lift capacity of the retreating blade. In other words, theeffective pitch'angle of the blade in forward and in rearward positionis substantially the arithmetic mean of thepitch angles of the bladewhen in advancing or in retreating relation. This arrangement utilizesthe lift capacity of the blades in their-fore aft;p0sitions'below fullcapacity, thereby further reducingtheefliciency of the rotor. There isno compelling reason for this additional lift capacityre- .Theretreating blade has a very small lift cayelocity relative to the air.:But this larger-cad duction. The lift production fore and aft issubstantially equal, and balance is provided at a lift production atfull capacity as well as at a lift production 'at' part capacity. It isa further object of my invention to'provid'e' a sustaining rot'orutilizing the lift capacity of the bladesin their fore and aft positionfullest without'regard to the lateral balance requirement. 1

The blades of conventional rotors change their effective angle ofincidence relative to the moving airrperiodically, once during eachrevolutionbf the blade. I have found that a more frequent change of the.incidenc angleQat least twice' during each blade revolution, and onewith an amplitude of the angle variation beyond that necessary for thelateral control greatly benefits the aerodynamic action of the blades,reducing the blade resistance and increasing the. blade lift capacity.It is a third object of my invention to provide a sustaining rotorhaving blades arranged to change their effective incidence angle.

periodically at least twice during each revolution of theblades withconsiderable amplitude variation. 7 These and other desirable objectsand advantages of the presentinvention will be illustrated in theaccompanying drawing and described in the specification, a certain"preferred embodiment being disclosed by way ofillustration only, for,

since" the underlying principles-may be incor porated in other specificdev1ces;it.is not intended to be limitedxtothe oner-hereshown; exceptasstructure I I aircraft.

Mo ses such limitations are clearly imposed by the ap-' the aircrafthaving said rotor hub assembly in? corporated, and

The hub assembly broadly designated'by I13 comprises a housing I 4fastened to the f-use'lage.

Asleeve I5 is mounted in said housing adapted to slide up and down andheld in vertical position relative to the housing by I screwfn'ieans 32'under the" control of the pilot, I A cam track drum" I1 is tiltablymounted on top of sleeve 'I5' by meansofa universal joint I6,

its'tilting position being controlled by means of control'lever I9'extending downwardly through the housing I4 and having its end adaptedto be manipulated or controlled by the pilot. Rotor hub 23'is mountedrotatably about a substantially vertical axis 'on-and aroundhousing I4.At its lower end it forms a gear wheel 24in mesh with the :gear wheel 25mounted on casing l l'and adapted to'be driven by an engine.

Blade roots 2B aremounted on the hub 23 tatable' about substantiallyhorizontal axes in atrailing edge 30. 'Theyrotate in clockwise di-"rection whenseen from above. The tail unitof the aircraft is broadlydesignatedby I2; 7 l

Blade roots 2IihaVe lever arms. projecting therefromin trailing relationto the blade ,mo-

'angle relative to the air.

the production of the lift, the former does not.. The flapping motionis-the outcome of an added,

4 about hinges 21, and this introduces a phase difference between thevariation of their pitch an-' gle and the variation of the effectiveincidence Th latter determines up effect of the lift produced and tendsto counteract 'or neutralize the pitch. This counteracting takes placewith time delay by virtueof the mass effects of the blades. Hence, inorder to obtain the largest effective incidence angle at the forward andrearward positions of the blades, it 7 Fig.7 4 represents a plan view'of'the rotor hub is necessary that the pitch an les have theirmaxassembly shown in Fig. 1.

imum at angular positions assumed after these forward and rearwardpositions have been passed by the blades. Ihave obtained excellentresults by arranging themaximum pitch'angles to take place at the 0 and190 azimuth position of the blades, with the forward position of theblade being considered at zero azimuth. That is to say, thebladeassumesthe maximum pitch angle as far as traceable to the sinuosityof the cam tion. Connecting rods 2| are hinged to said levers andguidedby rod guides 22 for upand down mo.- tion. Attheir upper. endstheyare provided with camfollowers 20. in operative contact with the camtrackIB of cam track drum ;II. Cam track I8 issinuous havingtwo valleysand two peaks,

as shown in Fig. 2. As the blades rotate, their pitch angle isperiodically changed in conserotation; Moving sleeve I5 by means ofscrew 32 changes the average pitch angle of the blades.

.Superposed to these known control and adjustment variations of thepitch angle isa periodic variation comprising two pitch angle increasesand two pitch angle decreases during each blade rotation. The amplitudeof this variation is governed by the amplitude of the sinuosity of thecam. track I8. I obtained excellent results by varying the pitch angleduring, each half revolution by plus andminus 3 /2 degrees It isessential for this invention that the blade produce its largestlift nearits mostforward position and near, its most rearward position relativeto the aircraft, and that it produce its smalltrack while occupying thefront quadrant and the rear quadrant of the blade rotation circle, moreparticularly while occupying thesecondhalf of these quadrants, the firsthalf of these quadrants having already been passed through by the blade.

This isv represented in the drawing. Since the levers 3| trail the roots26, contact of follower 28 with the lowest point of. track; I8 willproduce the highest pitch angle. The contact points trail the rootpositions by 45. Hence, the lowest pointof 1 track I 8 must be at ornear the azimuth positions 325 and 145. As indicated in Fig. 3, track I8of Fig; 2 is represented as seen by an observer 7 the portion of theblade course nearer the fuselage axis. f

1 i r (I 1. In an aircraft sustained by a bladed rotor having bladesmounted with freedom for flapping movement, and having controllablemechanism for shifting the line of action of therotor force to maneuverthe aircraft, automatic mechanism operative in different positions, ofadjustment; of

said controllable mechanismyto periodicallyvary the geometric pitch,angle *ofithe'blades, said automatic mechanism being constructed andarranged so as to impartmaximum increment of pitch angle to thebladesiwhile they are passing through the quadrants of. the circle ofrotation in forward and in rearward relation to the: aircraft.

2. In an aircraft sustained bya bladed rotorhaving blades mounted withfreedom for flapping movement, and having controllable mechanism forshifting the line of action of'the rotor force to maneuver the aircraft,automatic mechanism. operative in different positions of adjust- 'mentof said. controllable mechanism. to periodically vary. the geometricpitchangle of the blades,

est lift near its lateral position relative to the This 'does notnecessitate the. largest pitch angle'at'the fore and aft positionsnorthe said automatic mechanism being constructedand arranged so as toimpart maximum incrementof pitch angle to the blades while they arepassing through thequadrants of the circle of rotation in and aftertheyihavepassed positionp 3;stln"anaircra'ft, a sustainingretbrcoat-ssing a'hub rotatable about a substantially verti'-' cal axis, ablade root projecting substantially radially from said hub and mountedrotatably for variation of its geometric pitch angle, a blade hingedtosaid root, a slidable and. universally tiltable drum mounted in saidaircraft centrally to said rotor, a sinuous cam track in said drum, acam follower in operative contact with said cam track and in operativelinkage with said root, the cam track and the linkage being sodimensioned, arranged, and adjusted so as to impart to the blade amaximum increment of geometric pitch angle while it is passing throughthe quadrants of the circle of rotation in forward and in rearwardrelation to the aircraft.

4. In a rotary aircraft, a sustaining rotor hav- 6 ing radialvariable-pitch blades, a circuitous sinuous cam track with two valleyportions and two peak portions, and mechanism linking the cam track tothe blades constructed and arranged so as to cause automaticallyperiodic variations of the geometric pitch angle of the blades, so as toassociate a predetermined value of the increment of geometric pitchangle with each angular station of the blade, and so as to associate themaximum increment of geometric pitch angle of the blades with bladestations within the two quadrants of the blade rotation circle inforward relation and in rear relation to the aircraft.

S'I'EPHAN PAUL NEMETH.

